Today, several generations of radio communication systems have evolved in the world. The several generations of the radio communication systems includes first generation system (1G), second generation system (2G), third generation system (3G) and fourth generation system (4G). Each of the generations has different transmission characteristics and different communication technology.
The first generation system (1G), for example Advanced Mobile Phone System (AMPS), Total Access Communications System (TACS), is based on analog frequency modulation technology. Similarly, the second generation (2G) system, for example Global System for Mobile communications (GSM), is based on Time Division Multiple Access (TDMA). The third generation (3G) systems are based on a Wideband Code Division Multiple Access (WCDMA) air interface. Examples of a 3G system are Universal Mobile Telecommunication System (UMTS) and GSM Evolution (EDGE).
The fourth generation system (4G) is an ITU specification that is presently being developed for broadband mobile capabilities. The 4G system would enable Internet Packet (IP)-based voice data and streaming multimedia at higher speeds, compared to 3G. The radio communication system is also termed as Radio Access Networks (RAN). As the number of RANs is increasing, the geographical areas are also covered by one or more RANs. For example, at a given geographical area there may be two RANs that operate simultaneously, for example 2G and 3G systems. Similarly, there may be a geographical area where only one RAN is operating, for example only 3G.
Thus with an increase in the number of RANs, for example GSM, UMTS, Wireless Local Area Network (WLAN), and EDGE, interworking between different RANs and air interface standards has become a priority. Hence, to achieve efficient interworking between different RANs and to provide more network coverage to User Equipment (UE), handover procedures between RANs and communication network has become increasingly important. The Handover (HO) procedure is a technical procedure for switching an in-progress call from a coverage area of one base station (or one communication systems) to another base station (or another communication system) while ensuring the continuity of the in-progress call.
The HO in a communication system is when the UE moves from one radio cell supported by the communication system to another radio cell supported by the communication system. For example in 2G, moving from coverage area of one base station associated with one service provider to another base station supported by the same or different service providers. The HO between different RANs means an inter-technology handover, for example moving from a 3G network to a 4G network, and vise versa. The HO between different RANs is known as interlayer HO.
The different RANs have different characteristics and have different network structures that enable communication services for the UE. Hence, the HO procedures from one RAN to another RAN have to be managed efficiently. For example, voice bearers and non voice bearers that are associated with the UE in a first RAN can be supported through Packet Switched network and/or Circuit Switched network. Further, when the UE moves from the first RAN to a second RAN and HO procedure is initiated, and then there may be a case that the second RAN have different capabilities than the first RAN. Then the voice bearers and non-voice bearers associated with the UE have to be managed efficiently based on the capabilities of the second RAN.
Hence there exists a need to efficiently manage HO requests in Radio Access Network (RANs).